The disclosure generally relates to a power converter and, more particularly, to a control circuit applicable to the power converter using external resistors.
Power converters adopting the constant on time control scheme are widely applied in many fields since the constant on time control scheme has many advantages. In a conventional control circuit of the power converter, an error detection circuit is employed to detect the difference between a reference signal and a feedback signal, so that circuits in the subsequent stages can adjust the on time of the power switch according to the detection result of the error detection circuit.
In some power converters, the aforementioned feedback signal is generated by an external feedback circuit arranged outside the control circuit. The designer of the control circuit has to know the voltage-dividing ratio of the external feedback circuit used by a particular power converter and then adjusts the component parameters of the conventional control circuit in advance, so that the conventional control circuit can operate normally in the particular power converter. If the voltage-dividing ratio of the external feedback circuit can not be obtained before manufacturing the conventional control circuit, the conventional control circuit is not able to correctly estimate the magnitude of the output signal of the power converter through the feedback signal, and thus not able to correctly adjust the on time of the power switch.
In other words, the structure of the conventional control circuit is only applicable to particular power converters using the same structure of external feedback circuit, and not suitable to other power converter using an external feedback circuit having a different voltage-dividing ratio. Apparently, the application scope and application flexibility of the conventional control circuit are very restricted.